The Hydro Desulfurization and Cracking unit (HDC) is an important process unit within a petroleum refinery. The HDC converts heavy aromatic compounds, typically a combination of cycle oil and coker naptha feeds, into lighter products which can be blended into gasoline and jet fuels. The primary processing equipment for an HDC are multiple sequential fixed bed reactors (for hydrocracking and hydrotreating) and product fractionation columns. Due to the fast dynamics of the process, the highly exothermic kinetics of the reactions, and the large degree of interaction between the process equipment of the HDC, abnormal process operations can arise which cause the HDC to deviate from the normal operating state. Abnormal operations of the HDC can have significant safety and economic consequences. These situations can cause catalyst or equipment damage, lost production, environmental emissions, injuries or fatalities. A primary responsibility of the console operator is to identify the root cause of an abnormal situation and to perform corrective actions within sufficient time to avoid potentially severe consequences.
The current industry practice is to use a combination of base and advanced process control applications to automatically mitigate minor process disturbances. The current industry practice also relies on human intervention for moderate abnormal operations and automated emergency shutdown systems for severe abnormal operations. At present, the console operator is notified of the onset of an abnormal condition through process alarms. These alarms are triggered when key process measurements (temperatures, pressures, flows, levels and compositions) violate static operating ranges. This notification technology is challenged to provide timely alarms while sustaining an acceptable rate of false notifications when the key measurements are correlated for complicated processes such as an HDC.
For the typical HDC unit, there are in excess of 550 critical process measurements. Under the conventional Distributed Control System (“DCS”) system, the operator must survey the critical sensors presented in both tabular and trend format, validate the behavior against expected normal operating values, and discover potential problem(s).
Due to the large number of sensors in an HDC, the onset of abnormality can easily be overlooked. With the current DCS based monitoring technology, the only automated detection assistance an operator has is the DCS alarm system which is based on the alarming of individual sensors upon violation of predetermined limits. Due to the complexity and the fast dynamics of an HDC, this type of notification is often delivered too late to enable the console operator to have sufficient time to identify and take preventive action to mitigate the problem. The present invention provides a more effective notification to the operator of the HDC.